ELISA antibody test. Multi-well sample trays during an enzyme-linked immunosorbent assay (ELISA) antibody test. The ELISA test checks for antibodies to viral diseases such as AIDS (acquired immune deficiency syndrome), as well as hepatitis B and C. First, the patient's blood plasma is washed over a surface covered in the antigens of the virus being tested for. If the antibodies are present then they will bind to these antigens. Next, peroxidase is added which binds to the antibodies. Then a chemical is added that changes colour when it comes in contact with peroxidase.